A rule of thumb I received from the Taxpayer Advocate Service for any international tax issue: whether you are in the U.S. or abroad, mail your entire return including Form 8833 directly to the Austin Tax Center.
Internally, the IRS processes all international tax returns in Austin (i.e., any return with an address outside the 50 States + DC, that excludes foreign income, or that contains a “foreign” form such as 1040 NR, 2555, 8833, 1042, etc.—see IRM 3.11.3.6.2.13). This includes returns sent from inside the U.S. to any regional tax office; the IRS procedure provides that the processing agent “stop editing and immediately forward international returns—in their entirety—to AUSPC (Austin).” Even if you have a payment to make, the P.O. Box in Charlotte just receives the payment; the return is still forwarded to Austin for processing.
To reduce delays and to reduce the chance of a lost return, send the entire return directly to Austin. For greater efficiency, use a private courier service (UPS, FedEx, DHL, etc.) and send to the physical address, not the P.O. Box:
Austin—Internal Revenue Submission Processing Center
3651 S IH35,
Austin, TX 78741
